Major soilborne diseases in North Carolina and surrounding states include fusarium wilt (FW) (causal agent Fusarium oxysporum f. sp. lycopersici; all three races), verticillium wilt (VW) (Verticillium dahliae; two races), southern stem blight (SSB) (Sclerotium rolfsii), root-knot nematodes (RKN) (primarily Meloidogyne incognita) and bacterial wilt (BW) (Ralstonia solanacearum race 1), distributed across the subtropical to temperate ecosystems in the state.
FW, VW, SSB, and RKN can be well managed using standard fumigants.
Alternative management practices are needed in production systems where fumigants are not used or effective, and/or where heirloom tomato cultivars are grown.
We are involved in a USA multi-state program to determine the viability of grafting in open-field production systems.
Previously published work showed the utility of grafting to manage FW, SSB, RKN, and BW. In complementary work to manage BW, a replicated on-farm field trial demonstrates that fumigants such as Paladin (79% dimethyl disulfide + 21% chloropicrin) and PicClor60 (60% chloropicrin + 40% 1,3-dichloropropene) allow up to 80% plant death, similar to incidence in non-fumigated plots, whereas grafting to resistant rootstock (Seminis 'Cheong Gang') confers 100% control in non-fumigated plots.
Another on-farm randomized complete block design experiment demonstrated that three commercially available rootstocks conferred 100% plant stand, whereas non-grafted plants had 80% plant death using a round tomato scion ('Red Mountain') or 15% plant death using a roma tomato ('Picus'). Grafted plants show economic viability in North Carolina, and additional work is needed to optimize this tool in diverse production systems.